This disclosure relates to an engine mount for a gas turbine engine that includes an adjustable attachment feature.
Gas turbine engines are mounted to a pylon using a forward engine mount and an aft engine mount. The forward engine mount is mounted to a compressor case using a shackle with two connection points. The shackle reacts to both vertical and lateral loads between the engine and the pylon. The shackle is comprised of two identically shaped plates that are attached to each other such that a crack cannot propagate from one plate to the other, which satisfies a failsafe requirement for the shackle.
The compressor case includes two case holes that are to be aligned with two corresponding shackle holes in the two plates. Fasteners or pins are then installed in the aligned holes. The case holes and shackle holes are drilled and reamed as required to maintain fit specifications. In order to maintain interchangeability between the two connecting components, the position tolerance of the holes cannot accumulate to more than the minimum clearance allowed at the pinned joint. This is a tight requirement with significant associated cost.
To address this issue, the diameter of the holes in the case and/or shackle could be increased for a “loose” fit; however, this would result in a structural and weight penalty. As the pins are not tightly held within the holes due to the “loose” fit, one of the pins will be subjected to all of the engine's lateral loads before the other pin. The case and the shackle will then need to deform by a certain amount until the second pin banks against an edge of its hole and begins to share the load. This results in an unequal load share, which requires that the case lugs be designed for a high load, and thus have a higher weight.
Further, while the shackle is made from two plates to prevent crack propagation, additional failsafe requirements may not be met by the stacked two plate configuration. For example, a failure in one of the engine case lugs will compromise the vertical and lateral load paths.